Patterns are the start of learning algebra - because generalising number rules is a good way to start thinking about abstracting numbers and their relationships.

Websites

Good websites for teaching or practicing patterns

Famous Number Sequences

Interesting number sequences (you'll have to decide whether your students will cope with these)

Fibonacci Numbers

Pascal's Triangle

Interesting Number Pattern Facts and Ideas

Did you know that square numbers are the sum of the sequence of odd numbers? e.g. 9 is the sum of 1,3,5. 16 is the sum of 1,3,5,7. And so on. First written up by Fibonacci in his Book of Squares. See this 3 minute MathTV on YouTube for more info.